Switching systems



April 2, 1963 w. F. KosoNocKY E'rAl. 3,084,264

swITcHING SYSTEMS Filed 001'.. 30, 1958 2 Sheets-Shea?l 1 41 nnnnnnnnnnnn/gt my www/www- INVENTOR5 WALTER E KnsnN/DLKY LUBDMYR S. NYSHKEVYEH imam/fr 2 Sheets-Sheet 2 SWITCHING SYSTEMS W. F. KOSONOCKY ETAL Anf/mfr ffm/:vnr

INVENTORS WALTER P.' KusnNncKY By LUBUMYR S. Elms Kawai-1 /W/MIY United States Patent O 3,684,264 SWITCHING SYSTEMS Walter F. Kosonocky, Newark, and Luiromyr S. Onyshkevych, Princeton, NJ., assignors to Radio Corporation of America, a corporation of Delaware Filed Oct. 30, 1958, Ser. No. '776,830 Claims. (Cl. 367-83) This invention relates to switching systems, and particularly to switching systems using non-linear reactance elements.

It is known that parametric oscillations can be established in a resonant circuit using a non-linear reactance. This non-linear reactance may be magnetic, such as a ferromagnetic core, or may be capacitive such as a ferroelectric condenser, a variable capacity diode, and so on. Circuit oscillations occur in either one of two distinct phases. Thus, the circuit is a bistable circuit with rcspect to the phase of oscillations. The two phases are used to represent the two binary information signals 1 In many applications, it i-s desirable to provide a bistable circuit that can Ibe :simply and reliably changed from one stable state to the other each time an input signal is received. For example, in scaling and counting circuits, in triggerable flip-flop circuits, in complementing circuits, and in logic in circuits, and so on. Each input signal causes the circuit to reverse its present state.

An object of the present invention is to provide improved storage `systems using parametric oscillator circu-its.I

Another object of the present invention is to provide improved bistable circuits which are triggerable from one stable state to the other stable state in a simple and reliable manner.

A further object of the present invention is to provide improved methods of and apparatus for switching the phase of oscillations and parametric circuits.

Still another object of the present invention is to provide novel methods of and apparatus for changing the phase of a parametric oscillator circuit.

According -t-o the present invention, the parametric oscillator circuit operates .at a fixed multiple which term, as used herein, includes sub-multiples and the fundamental of the A.C. supply frequency and in one of the two phases. The natural frequency of the resonant circuit is somewhat different from the multiple frequency. By suitably modulating the A.C. (alternating current) supply signals, theI frequency of the circuit oscillations changes from the fixed frequency towards the natural frequency of the resonant circuit. This natural frequency is determined by the physical parameters of the reaotance elements used in the circuit, and in practice, is different from the multiple frequency fixed by the A.C. supply. Thus, depending upon the length of the modulation interval, the oscillations in the resonant circuit gain or lose an even or an odd number of half cycles with respect to the parametric oscillation frequency. These resonant circuit oscillations effectively function in the same manner as the externally applied control signals of the prior art circuits. Thus, if the resonant circuit has gained (or lost) an odd number of half cycles, the parametric oscilla-tions are restarted in the phase opposite the one phase. If the resonant circuit has gained (or lost) an even numer of half cycles, the parametric oscillations are restarted in the same one phase.

yIn the accompanying drawings:

FIGS. l and 2 are, respectively, schematic diagrams of two different forms of parametric oscillator circuits useful in the present invention;

3,084,264 Patented Apr. 2, 1953 ICC FIG. 3 is a graph of the response characteristics of the circuits of FIGS. 1 and 2 as a function of A.C. supply amplitude;

FIG. 4 is a timing diagram of waveforms useful in explaining the operation of the system of FIG. l;

FIG. 5 is a schematic diagram of a parametric oscillator circuit according to the invention using a pulsed A.C. modulation source;

FIG. 6 is another timing diagram further explaining the operation of the circuits of FIGS. l and 2 according to the present invention; and

FIG. 7 is a graph of curves showing the circuit switching time as a function of A.C. supply frequency.

Parametric oscillator circuits frequently use a pair of non-linear reactance device-s connected in a balanced tuned circuit relation with a linear reactance element. The pair of devices operate to balance out the A.C. supply signals from the circuit output. The non-linear reactances may be a pair of magnetic cores or as shown in FIG. 1, a pair of variable capacity diodes 21 and 22. The diodes 21 and- 22 may be junction diodes which exhibit a variable capacity when biased in the reverse direction. The diode 21 has its anode connected in series with a first A.C. supply winding 23 to a reverse 'bias -source such as a battery 2d. The positive terminal of the battery 2liis connected t-o a common point or reference potential indicated in the drawing by the conventional ground symbol. A bypass capacitor 25 conveniently is connected across the terminals of the battery 24 to prevent transient signals from affecting the bias point of the diode 21. The cathode of the diode 22 is connected in series with a second A.C. supply winding 27 to the positive terminal of a reverse bias source shown as a battery 28. The negative terminal of the battery '2S is connected to ground. A separate bypass capacitor 29 is connected across the terminal of battery 28. The cathode of the diode 21 and the anode of the diode 22 are each connected to a common junction point 3).

The linear reactance in the circuit of FIG. l is provided by an inductor 31 having one terminal connected to the common junction 3d' and the other terminal connected to ground. An output device 32 is connected across the inductor 31. A.C. signals are applied to the oscillator circuit by means of a transformer 33 having the first and second A.C. supply windings 23 and 27 as its secondary windings and having a primary winding 34 connected to the outputs of an A.C. supply source 35. A modulating circuit 36 is connected between the A.C. supply source 35 and the primary winding 34 of the transformer 33 to modulate the A.C. supply signals in a desired fashion. The modulator circuit 36 may be one capable of modulating the amplitude of the A.C. supply by such as the single-pole, single-throw switch 37. Other known types of amplitude modulating circuits may be used.

Another form of oscillator circuit 20 using variable capacity diodes is shown in FIG. 2. The circuit 20 is similar to the circuit 2l) of FIG. 1 except that the pair of A.C. signal windings 23, 25 of FIG. l are combined in a single center-tapped secondary winding 4d. The diode 21 is connected to one terminal of the secondary winding it? and the diode 22' is connected t-o the other end terminal of the secondary winding 40. The center tap of the secondary winding 4t) is connected to the common junction point 3d.

In operation, application of A.C. supply signals of sufficient amplitude to the circuit 2d causes the circuit Ztl to begin oscillating parametrically at a multiple of the supply frequency and in either one or the other of two opposite phases. When variable -capacity diodes are used, the second subharmonic of the A.C. supply frequency is used because the energy conversion between the supply and the output circuits is most efficient at this frequency.

-tude control Isignals of the desired phase.

Normally in the absence of `an additional control signal, the phase in which the circuit 2.@ oscillates is undened. That is, the phase of a random noise signal occurring at the V-startof the build-up ofthe parametric oscillations determines the phase of the circuit oscillations. ln the prior art circuits, an additional control signal' at the subharr'nonic frequency and of the desired phase is coupled to the circuit 29. The amplitude of the control signal is made larger than that of the random noise. This control signal insures that the parametric oscillations occur in the desired phase.

The waveformsof lirics ajb, yandc of FIG. 4 represent the AJC. supply signal of frequency (2f), the control signals of the subharmonic frequency (f), and the output signals at the frequency (f). The control signals are applied in either one or the other of the two phases represented, respectively,1by the solid curve 42 and the dotted curve 43 :of line' b. The control signals are also applied at a time just prior to the yapplication of AC. signals represented by the solid curve i4 of line a. In the absence of A.C. supply signals, relatively little or no output signal is produced iby the circuit 20. When the A.C. signals 4are iirst applied, theoscillationjs begin to build up exponentially in the same phase as the previously applied control signals, as represented by the solid curve 46 and the dotted curve 47 of line c. After the oscillations have reached a maximum amplitude, the control signals may be removed and the circuit will continue to operate in the set phase.

When it is desired to change the phase of the oscillations of the circuitd, the A.C. supply signals are first removed, a new control signal in the desired phase is then applied, and finally, the AJC. signals are again applied "withv the circuit oscillating in the new phase.

Other methods of reversing thephase of the circuit oscillations include applying two relativelyy large ampli- These two signals I.together cause the circuit oscillations to die out and then -begin again in the desiredphase. Still another method is to reduce the amplitude of the A.C. supply signals and apply an additional control signal of suitable amplitude. This .additional control signal together with the reduced amplitude supply signals forces the oscillator circuit to assume the desired phase. Thus, in each of the prior ait circuits, the changing of the phase of the oscillator circuit involves the application of one or more externally applied control signals.

AThe response curve 39 of FIG. 3 represents the oscillator output voltage asa function of A.C'. supply voltage amplitude. As shown by the curve 39, the parametric oscillator circuit exhibits three distinct response regions, designated I, lI, and III, with increasing supply amplitude. yIn taking the curve 39, the supply frequency is lixed, as is the circuit'tl tuning. In region I, between the points o Vand a, the circuit is not oscillating and substantially no output voltage is produced. As the A.C. supply increases from the point a to the point b circuit suddenly jumps into oscillation at the point b and the output voltage rises sharply to a value indicated by the point c of the curve 39. As the supply voltage increases from the point b` to the point d in the region III, the circuit continues oscillations until the point d is reached. For sup ply amplitudes in excess of that corresponding to the point d, the circuit can no longer sustain the parametric oscillations and the output voltage remains substantially at value. When the supply amplitude decreases from the point d, the circuit continues operating in the region III and in the region vIl until the point e is reached. At the point e of the curve 39, the circuit ceases oscillation and the output voltage sharply Adecreases to 0i value. Thus, the region II, between the points a, b, c, e, is one having a hysteresis eifect. Observe, however, that the circuit can only oscillate for ranges of the supply voltage amplitude between the points a and d along the abscissa.

It the supply voltage `amplitudeV is made lower than that corresponding to the-point a, say that indie-ated by the point S2, the circuit ceases oscillation if -it were previously oscillating or does not begin oscillating if it were previously not oscillating. Similarly, for supply voltage amplitude in excess :of the value d represented by the point S3 along abscissa, the circuit, if it were previously oscillating, ceases oscillation. Normally, the supply'voltage amplitude is maintained at a value corresponding to the point Sl of which a maximum output voltage is obtained with the circuit response being in the region III of the characteristic.

The oscillator circuit 2,0 of FIG. 5 is the same as the oscillator circuit Ztl of FIG. 2 except lthat a diffrent modulation source 36"is used. The modulation source 36 may be any suitable source arranged to apply a burst of alternating current signals in thefrequency 2f to the oscillator circuit 26". The output of the oscillator circuit 36 is transformer coupled to the secondary winding 40 by means of an additional primarywinding'YlS of the transformer 33". The modulation source 36, Vfor example, may be another parametric oscillator circuit arranged'to' apply a burst of output pulses of either one or the other of the two phases and 'atthe supply frequency (2f) to the primary Winding`48. "If the burst of modulation output pulses is in the one phase, the net A C.

vsupply of the oscillator'circuit 20 is changed from the Vpoint represented byV S1 of FIG. 3 to that represented by the point S3. Accordingly, the circuit 20 stops oscillating for the duration of the burst of output pulses from the modulator 36. If the vburst of output pulses from thev modulation'source 36 is of the otherphaSe, the net A.C. supply applied to the oscillator 20" changes from the point represented by S1 in FIG. 3 to the point represented by S2 of FIG. 3. Again, the circuit 20 ceases operating parametrically for the duration of the modulation burst. The duration of the modulation burst is controlled `by` two control pulses 49, 50 applied to a control input 51 of the modulation source 36. The first control pulse 49 is applied between a time to and a later time t2. The second control pulse 50 is applied between the time t0 and the time t3 with the second control pulse being of relatively longer duration. The reason for the different duration control pulses 49 arid 50 is described more fully hereinafter kin connection with FIGS; 6 and 7. The modulation source 36 may be a'parametric oscillator burst generator as described, for example, in our copending application, Serial No. 765,876, led October 7, 1958, entitled Switching Systems.

In FIG. 6, the waveforms of lines d, e, f, g, h, z' and 1' represent the selective switching of the phase of a para- `metric oscillator circuit using the modulating circuit 36 of FIGS. 1 and 2. The A.C."supply waveform is shown in line d of FIG. 6. 'In lines e and h, there is shown the envelope of the A.C. supply waveform amplitude modulated l00% by the modulating circuit 36. Lines and respectively,`represent output waveforms in`which the phase of the circuit' oscillations is and is not changed `due to the supply modulations. The waveforms of lines g and j of FIG. 6 are reference waveforms at the output frequency (f), and are used as an aid in illustrating the switching of' the Vphase of the output waveforms of lines f and i.

IConsidering now,`lines e, f, and g of FIG. 6 assume that at time to, the A.C. signals are applied as by closing the switch 37 of the modulating circuit 36. Also assume'that the oscillator circuit '20 is operating in the same phase as the reference waveform of line g. At time t1, the switchy 37 of the modulator circuit 36 is opened, `and at fthe later time t3, the switch 37 is again closed. At the time r1 when the switch 37 is opened, the oscillations in the circuit 20 begin to die out exponentially due to the absence of the A.C. supply. Also, the oscillation frequency starts to change towards the natural frequency ofthe tunedA circuit. In practice, the natural frequency is made slightly higher than the parametric oscillating frequency. Thus, for example, the oscillator 20 may be set for parametric oscillations at two megacycles using a four megacycle A.C. supply source 35, and the oscillator circuit natural frequency of 2.8 megacycles. In such case, between the times t1 and f3, the oscillation frequency of lthe circuit 20 begins to increase towards the natural frequency. Thus, as a function of time, the phase of the oscillator output, line f, begins to lead the phase of the reference waveform, line g. The time interval t1-t3 is chosen such that the oscillator phase leads the reference phase by approximately 360, or by -two half cycles. Thus, at the time t3 the oscillator output waveform is again in phase with the reference waveform of line g. Now at the time t3, when the A.C. supply is again applied as by closing the switch 37, the oscillator begins to oscillate parametrically in the same phase as the reference waveform. Accordingly, when an even number of halfcycles of the parametric oscillation frequency are gained or lost during the modulation time interval, parametric oscillations begin again :in the initial phase. in digital terms, this corresponds to the same information being stored in the oscilla-tor 20 both before and after the modu- :lation interval.

Now, referring to lines h, z' and j of FIG. 6, the circuit waveforms are shown for a modulating interval between the times t1 and t2, the time interval t1-t2 being shorter than the time interval t1-t3. As shown in lines i and j of FIG. 6, the phase of oscillations of the circuit 20l gains 180 or one-half cycle over the reference waveforms. Accordingly, at the time t2, when the A.C. signals are again applied, as by closing the switch 37, the parametric oscillations build up in the opposite phase from the initial phase. Thus, when the A.C. supply source is modulated so that the resonant circuit oscillations gain (or lose) an odd number of half-cycles, the phase of the parametric oscillations reverse. In digital terms, this corresponds to the information previously stored in the oscillator 20 being complemented That is a binary l is changed to a binary 0, and vice versa.

The curves of FIG. 7 represent a plot of the A.C. supply frequency vs. the modulation time. The two shaded areas 60, 62 of FIG. 7 represent the reversal of of phase of the parametric oscillations due to the gaining of one-half and three halves cycles respectively during the modulation interval. Other shaded areas above the area 62 occur for gains of five-halves, seven-halves cycles, and so on. The shaded area 66, at the extreme right of FIG. 7, represents the reversal of phase of the parametric oscillations due to the losing of an odd number of halfcycles during the modulation interval. The unshaded areas of FIG. 7, between the abscissa and the shaded areas 60 and 66, represent the regions in which no or an even number of half-cycles are gained or lost during the modulation interval. The area between the abscissa and and the shaded area 60 represents the gain of less than a half cycle; `and the area between the shaded curves 60 and 62 represents the gain of two half-cycles. The point n along the abscissa corresponds to the value of A.C. supply frequency at which the parametric oscillation frequency and the natural frequency of the circuit 20 are equal. Thus, for values of A.C. supply of frequency n the circuit 20 continues to oscillate at the same frequency even during the modulation interval. Thus, no phase changes occur and no phase reversal is possible at the A.C. supply frequency n For A.C. supply frequencies producing parametric oscillations below the natural frequency "n, the circuit oscillations gain in phase during the modulation interval. For A.C. supply frequencies producing parametric oscillations above the natural frequency n the circuit oscillations lag in phase during the modulation interval. However, a cut-olf region, indicated by the dotted line, occurs slightly above the natural frequency "n when the A.C. supply frequency is too high to sustain parametric osciltations. The shaded region 66 is bounded on the extreme right by this cut-off region. Each of the regions is bounded by an upper and a lower curved line. IFor the shaded regions, the lower curved line represents the condition when Ithe circuit oscillations have gained say slight- =ly more than and the upper curved line represents the condition when the circuit oscilla-tions have gained slightly less than 270. Recall that the parametric oscillations can occur only in the two phases and the circuit will lock into the one of these two phases which is nearest to the control signal. -ln the present invention, the phase control is provided by the damped oscillations occurring in the tuned circuit during the modulation interval. The conditions when the circuit oscillations have gained exactly 90 or exactly 270 are conditions of uncertainty where the parametric oscillations could restart in either one :or the other of the two phases. This means that the modulation interval is not critical and any interval during which ya phase gain of say to 260 occurs can be used. Thus, if the modulation interval is set to cause a gain of 180, a tolerance of 70 is permitted without unduly alfecting circuit operation. Similarly, a wide tolerance is permitted in the other modulation interval when it is not desired to change Ithe phase of the oscillations, as indicated by the unshaded area between the shaded areas 60 and 62.

Observe also that the tolerance of the modulation interval increases as the parametric oscillation frequency approaches the natural frequency of the tuned circuit. The different ordinate value between the two extremes of a region becomes smaller as the A.C. supply is reduced a frequency. Below the bottom portion of lthe region 60', the modulation interval is of insufficient duration to permit the circuit oscillations to gain an appreciable portion cf a half-cycle with respect to the reference frequency. Accordingly, the circuit oscillation always restarts in the same phase when the A.C. signals are reapplied.

`Between the lower region 60 and the upper region 62, the circuit gains a full cycle and resumes operation in the same phase when the A.C. signals are reapplied.

The width of the upper shaded region `62 is narrower than the width of the iower shaded reg-ion `60, since in the upper region 62 the circuit is gaining three half-cycles.

'There have been described herein novel parametric oscillator switching systems in which an oscillator either switches or not `from a standard phase depending upon the time of interruptions of the A.C. supply signals. The switching is unconditional, that is, the oscillator always begins oscillating in a desired one of the two phases controlled by the interruptions of the supply signals. This switching feature may 'be incorporated in various known switching and memory systems in place of the additional control signal of the prior art circuit. For example, in memory systems using parametric oscillator circuits, the information may be read out of an oscillator circuit using the method of the present invention to insure that no stored information is lost during the read-out process.

What is claimed is:

l. A system comprising a parametric oscillator circuit having a natural resonant frequency, said circuit having different phases of oscillation respectively corresponding to dierent information signals, said circuit oscillating at a fixed multiple of an A.C. supply `frequency only when said A.C. supply signals of an amplitude within a given range are applied to said circuit, a modulating means connected to said circuit, and means for storing a desired information signal in said circuit including means for operating said modulating means to modulate said A.C. supply signals -to an amplitude outside said given range for a given time interval, said circuit resuming oscillations in one or the other of said phases in accordance with the duration of said given time interval.

2. A system comprising a parametric oscillator circuit having a natural resonant frequency, said circuit reprcsenting the two binary `digits by two diiferent phases of oscillation at one frequency which is a fixed multiple of an A.C. supply frequency Iand which different from said resonant frequency, said 'circuit oscillating at said one frequency'when A.C. supply signals are applied, a modulating meansconuected to said circuit andmeans 'for operating said modulating means to effectively cause said A.C. supply signals to change from an on condition to an ofrcondition for a given time interval, said circuit foperating at a frequency different from said-one frequency during said ot condition, and said circuit resuming oscillation in one or the 4other of said two phases in accordance with the length of sa-id'given time interval.

3. A system comprising a parametric oscillator circuit having a natural resonant frequency, the two binary digits being represented respectively by two phases of oscillation of said circuit, means for coupling A.C. supply signals to Asaid circuit, a modulating means coupled with said A.C. supply signals to said circuit, and means for operating said modulating means to modulate said A.C. supply signals for a given time interval to change the phase of oscillation of said circuit from one to the other of said two phases, said circuit resuming oscillation in one or the other of said twoy phases in accordance with the 'duration of said given time interval.

`4. In a switching system, the combination of a parametric oscillator circuit having a natural resonant fre* 25 quency and having two distinct phases -of oscillation at another frequency When A.C. `supply signals are applied to said circuit, said other frequency being a xed multiple of said supply frequency and being dierent from said resonant frequency with modulating means for interrupting said other frequency oscillations fora givenltimeinterval, said circuit resuming oscillations in one 'or the other of said two phases depending upon the lengthof said given time interval.

S. Asystem comprising a parametric oscillator'circuit Vhaving a natural resonant frequency, the two binary digits beingV represented by two distinct phases of oscillation `.at anotherfrequency whichis a xed multiple of an A.C. supply frequency and which is different from said resonant frequency, means -for applying said A.C.

signals to ysaid circuit, and means for applying momen Atarily to said circuit modulating signals at the frequency of and in a direction'to cancel said `A.C. signals, said circuit changing or not changing from one to theother of said two phases depending onthe duration of said modulating signals.

References Cited inthe file of this patent OTHER REFERENCES Article `by Turner in Radio-Electronics, May 1958, pp. 57-5'9. 

1. A SYSTEM COMPRISING A PARAMETRIC OSCILLATOR CIRCUIT HAVING A NATURAL RESONANT FREQUENCY, SAID CIRCUIT HAVING DIFFERENT PHASES OF OSCILLATION RESPECTIVELY CORRESPONDING TO DIFFERENT INFORMATION SIGNALS, SAID CIRCUIT OSCILLATING AT A FIXED MULTIPLE OF AN A.C. SUPPLY FREQUENCY ONLY WHEN SAID A.C. SUPPLY SIGNALS OF AN AMPLITUDE WITHIN A GIVEN RANGE ARE APPLIED TO SAID CIRCUIT, A MODULATING MEANS CONNECTED TO SAID CIRCUIT, AND MEANS FOR STORING A DESIRED INFORMATION SIGNAL IN SAID CIRCUIT INCLUDING MEANS FOR OPERATING SAID MODULATING MEANS TO MODULATE SAID A.C. SUPPLY SIGNALS TO AN AMPLITUDE OUTSIDE SAID GIVEN RANGE FOR A GIVEN TIME INTERVAL, SAID CIRCUIT RESUMING OSCILLATIONS IN ONE OR THE OTHER OF SAID PHASES IN ACCORDANCE WITH THE DURATION OF SAID GIVEN TIME INTERVAL. 